There is one edge we know of - our horizon, which is the limit of how far we can see.

Imagine sailing on a boat on the ocean and seeing a horizon in the distance, past which you know there is more Earth, but you just can't see it. We've measured the universe to be flat (as opposed to curved like Earth or saddle-shaped), but our horizon exists because of the finite speed of light.

Beyond that visible horizon, we think the universe just keeps going in the same way - forever.

We have no reason to believe there is an edge. But we also have no way of measuring this infinity because we physically cannot see it.

Only 5 per cent of the universe is made of ordinary material like planets, stars, cars, and coffee. This "normal matter" is made mostly of protons, neutrons, and electrons.

Another 24 per cent is an exotic material that interacts through gravity, but produces no light, making it invisible to us. We call this "dark matter".

While dark matter only interacts with normal matter very weakly, particle physicists have plausible candidates for what dark matter is.

Hopefully particle accelerators like the Large Hadron Collider will provide more insight for scientists very soon.

That brings us to the final 71 per cent of the stuff in the universe, which is a truly bizarre type of matter. Perhaps it's not matter at all, but a property of the universe itself. We call this mysterious stuff "dark energy".

What we do know is that dark energy has a gravitationally repulsive effect that is causing the expansion of the universe to speed up. But we don't understand how this acceleration is happening.

The universe has been expanding ever since the Big Bang 13.8 billion years ago.

But the Big Bang should not be imagined as a normal explosion in space. Rather, the Big Bang is an explosion of space itself, so that every point in space expands equally away from every other point in space. There is no centre to the expansion.

From our galaxy we measure that all galaxies are moving away from us, and the farther the galaxy, the faster away it is moving.

The interesting thing is that if you zoomed off to any other galaxy in the universe, you would measure the exact same effect - all other galaxies would be moving away from you.

In this way, you could argue that you are the centre of the universe. But then, so is everyone else.

When we look at distant galaxies, we are actually looking at a snapshot of the past.

Some galaxies are located so far away their light takes billions of years to reach us, even travelling at the speed of light. The images we collect through our telescopes tell us what the galaxies looked like billions of years ago, when the light left the galaxy.

Andromeda is the nearest spiral galaxy to our Milky Way. It floats at a distance of 2.5 million light-years, so the views we capture of Andromeda show us what it looked liked 2.5 million years ago. And that's the closest spiral galaxy.

The farthest galaxy we have detected is 13 billion light years away. This means we are looking at galaxy light as it was only 2 billion years after the Big Bang.

We will never capture light from the future though, only the distant past.

We are currently in the Stelliferous Era - meaning the universe has a lot of stars. This era began a few hundred million years after the Big Bang when the very first stars formed.

Now, almost 13.7 billion years later, new stars continue to form, although the number of new stars forming each year is dropping.

Eventually, new stars will stop forming and all stars will slowly burn out. But in that very distant future, supermassive black holes will still thrive.

It's believed that nearly every galaxy in the universe has a supermassive black hole at its centre, which means that eventually hundreds of billions of supermassive black holes will be spread throughout our ever-expanding universe.

Over trillions and trillions and trillions, and many more trillions, of years these black holes will slowly evaporate through Hawking Radiation.

The leftover elementary particles will be left to zoom through a vast, cold space with nothing much around to bump into.

3 comments:

Anonymous
said...

If the raisin bread theory is correct regarding the expansion of the universe, how come there are still galaxies colliding in space? By definition if everything were expanding away in equal distance and direction, essentially they are parallel and would never collide...

As an astronomer I already know all of these things, but they never make me feel small. Why? Because the human brain was somehow able to figure all of this out. My body may be small, and like all human beings I am deeply flawed, yet somehow this vast and extraordinary universe can fit into our heads.